1. Field of the Invention
The present invention relates to a key structure which is applied to a key having a wood part, and a keyboard apparatus including the key structure.
2. Description of the Related Art
Conventionally, key structures are known which are mounted in a keyboard apparatus and function as a key pivotally moved by key depression and for which wood or the like is used, as disclosed in Japanese Utility Model Registration Publication No. 2514485 and Japanese Laid-Open Patent Publication (Kokai) No. 2903959. In such a woody key structure, a wood material is used at least for a so-called “visible part” which is visible from the outside during both performance and non-performance, and the key structure presents a woody appearance and hence a high-quality appearance.
However, the conventional key structures have the following problems:
(1) Functional parts for realizing the key operation of each key (e.g. a key return spring, a key switch actuator, a key retainer), and other functional parts for urging the key and a hammer against respective pivots associated therewith, such as a spring having an S shape in side view, are usually provided between the key and a frame of the keyboard apparatus. Therefore, to arrange these functional parts, it is necessary to secure a certain amount of mounting space mainly in a vertical direction.
To this end, if the key structure is of a general resin-made type, it is easy to form a complicated shape, and therefore it is also easy to secure the mounting space for the functional parts. However, the woody key structure usually has its shape formed by machining, e.g. by being cut out of solid wood. Therefore, it is not easy to secure the mounting space for the functional parts. This makes it necessary to set wide spacing between the key and the frame, so that the total height of the keyboard apparatus becomes high, which is contrary not only to the demand for reduction of the size, but also to the demand for reduction of the weight since the amount of wasteful wood part increases.
(2) Further, in general, to provide functional parts formed separately from the key structure, such as a key guide, a sensor, and an LED, on the keyboard apparatus, it is necessary to provide recesses for accommodating such functional parts in the keyboard apparatus. Particularly in the case of woody key structures, it is sometimes necessary to provide such recesses in the wood part thereof. However, if the recesses are small, the dimensions and types of functional parts which can be mounted are limited, which lowers the freedom of mounting.
On the other hand, the key guide needs to have sufficient strength to fully perform its function, and particularly, it is preferable to design the key structure such that the width in the direction of juxtaposition of keys is increased, and the width of the associated recess for the key guide needs to be increased accordingly.
However, if the width of such a recess formed in the wood part is too large, the thickness of side walls of the wood part of the key structure, i.e. the thickness of portions between the recess and key side surfaces is reduced. If the thickness is reduced to about 1 mm, special working means, such as attachment of a reinforcing plate, has to be provided during machining of the woody part for adjustment of the key width, or it becomes difficult to machine wood under proper cutting conditions suited to the machining of the wood.
Further, normally, lubricant is provided between the key guide and the recess, for reduction of sliding frictions. However, if the lubricant is directly applied to the recess formed in the wood part, there arises not only the problem that the lubricant enters the wood part to discolor the wood part, but also the problem that the lubricant eventually stops functioning properly due to dispersion and deterioration thereof.
(3) By the way, in the woody key structure, the wood part is disposed on the top surface of an elongated key base body or on the lower surface of an upper plate member, and fixed to the key base body and/or the upper plate member by an adhesive. Further, in the case where a front butt end member is disposed at a front end (an end toward the player) of the key structure corresponding to the front butt end of the key, it can be envisaged that the front butt end member is provided in fixed relation to the upper plate member or bonded to the front end face of the wood part by an adhesive.
However, the wood part expands and contracts or deforms due to changes in environmental conditions (humidity, temperature, aging, etc.), and therefore, if the key base body and the front butt end member are formed integrally with each other, or they are formed in separate bodies but substantially in contact with each other when the key structure is manufactured, the two members may interfere with each other due to expansion and contraction or deformation of the wood part, which degrades the fixation of the wood part to the two members, and in the worst case, separation of them occurs. Further, in a keyboard apparatus having an upper plate member, if the wood part is secured to the upper plate member and at the same time the front butt end member is provided in fixed relation to the upper plate member, the fixation of the wood part to the upper plate member is degraded due to expansion and contraction, or deformation of the wood part. If the fixation of the wood part to the upper plate member, the key base body, or the front butt end member is degraded, the front end of the key can become faulty. Thus, required durability of the key cannot be ensured.
Further, a keyboard apparatus in general is provided with a limiting member, such as a stopper, for limiting a key depression end position. The limiting member is preferably provided at a location where the front end of each key is brought into contact therewith so as to provide the highest limiting effect. However, if the limiting member is disposed below the front end of the key and the front butt end member is disposed in contact with the limiting member, the fixation of the wood part to the front butt end member is degraded due to a shearing force applied between the front butt end member and the wood part as the key depressing operation is repeatedly carried out. Moreover, in the case where the keyboard apparatus has an upper plate member, if the wood part is secured to the upper plate member, and at the same time the front butt end member is provided in fixed relation to the upper plate member, the fixation of the wood part to the upper plate part is degraded due to the repeated key depressing operations. When the fixation of the wood part to the upper plate member or the front butt end member is degraded, the front end of the key can become faulty. Thus, required durability of the key cannot be ensured. On the other hand, if the limiting member is disposed at a location closer to the rear end of the key so as to prevent the key from being brought into contact with the front butt end member, the limiting function is weakened due to a change in the lever ratio, which makes it difficult to perform a proper limiting operation.
Furthermore, in addition to giving a woody appearance, the minimizing of the area where the wood part is disposed contributes not only to saving of the expensive material but also to reduction of the weight of the key itself, and therefore it is essential to design the key structure while considering the relationship between the front butt end member and the wood part in view of these merits.
(4) By the way, there is also conventionally known a key structure applied to keys of a keyboard apparatus, in which wood is used as a base material and the surface (top) of the base material as the depressing surface of the key is coated with resin or the like. However, although the key structure having resin or the like coated on the surface of the base material gives a high-grade texture due to the wood being used as the base material, this key structure is more difficult to machine compared with the resin-based key structure, and therefore it is difficult to manufacture key structures uniform in quality at low costs.
(5) Further, wooden keys originally designed for acoustic pianos are often also used for manufacturing the woody key structure, since they are easily available. The key structure is normally provided with not only a pivot about which the key is moved and a guided mechanism for being guided by a key operation guide, but also an engaging part (“associated element-engaging part” or “key functional part”) for driving an associated element, such as a mass member or a key switch, and an engaging part for engaging an associated element. However, if these engaging parts are made of wood, high machining tolerances cannot be required of driving sections thereof, due to the limited accuracy of woodworking. On the other hand, if the key structure is made of resin or the like as a one-piece member including the pivot and the engaging parts, a woody appearance cannot be obtained at all, and further, the touching feeling tends to be adversely affected since the rigidity of the resin key is lower compared with the wooden key.
(6) Further, in this type of key structure, “the associated element-engaging parts” and “the key functional parts” are also often formed at the wood part by machining the same, and therefore the freedom of design concerning the functions and shapes thereof is low, and the machining accuracy is low with lots of limitations on machining. This makes it difficult to exhibit the key functions with high accuracy.